Human cytomegalovirus (HCMV) is an important cause of morbidity and mortality among immunosuppressed individuals. A deeper understanding of the elements involved in the human T cell immune response to this virus is vital to enable the development of vaccines to HCMV. T cell recognition of foreign antigens is determined in part by the ability of antigenic peptides to bind to molecules of the major histocompatibility complex (MHC) which are highly polymorphic cell surface glycoproteins. T cell recognition is mediated by the formation of a ternary complex between antigenic peptides, MHC molecules and the T cell receptor (TCR). Allelic variation of MHC molecules greatly influence the spectrum of antigens that an individual can respond to. Studies of specific antigen systems in the mouse have revealed that TCR gene elements are also critical in determining the antigen fine specificity of a T cell response. Thus, genetic variation at both the MHC locus and the TCR loci will influence T cell responses. This study aims to investigate, in detail, the T cell response to HCMV. Individuals will be selected who have previously been exposed to HCMV. These individuals will be HLA typed by standard serological techniques and by the molecular techniques of the polymerase chain reaction (PCR) and dot blot analysis with allele specific oligonucleotide probes. Responsiveness to purified HCMV proteins will be assessed in these individuals. HCMV specific T cell clones will be generated from individuals who respond to particular proteins. The T cell clones will be analyzed for their antigen fine specificity in terms of which HCMV proteins are recognized. Using previously defined algorithms, peptide sequences will be identified as epitopes for these T cells. The MHC restriction of these clones will be analyzed by monoclonal antibody blocking studies and mouse L cells transfected with the appropriate MHC molecules. The TcR alpha and beta chain genes being used by such well characterized T cell clones will be analyzed in detail. This will be done either by the construction of cDNA libraries followed by cloning and sequencing of isolated TCR alpha and beta chain genes or by anchored PCR amplification of the V-C junctional regions and sequencing of this region. These studies will allow greater understanding of the genetic elements in the human T cell mediated immune response to a specific virus. CMV infection is a major problem in organ transplant recipients. The University of Pittsburgh is a major center for liver transplantation. This study will also aim to identify possible HLA associations with manifestations of CMV infection, in patients undergoing liver transplantation which are likely to have an immunopathological component. These will include CMV hepatitis, CMV infection occurring in conjunction with graft rejection and CMV interstitial pneumonitis. These studies could lead to an enhanced ability to identify patients at risk for developing life threatening CMV infections following liver transplantation.